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Strangeness Production in p+p collisions at 200 GeV. Mark Heinz University of Bern, Switzerland For the STAR collaboration HotQuarks Taos NM, July 2004. Contents. Motivation STAR Results Experimental comparisons PYTHIA comparisons Summary. Motivation.

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strangeness production in p p collisions at 200 gev

Strangeness Production in p+p collisions at 200 GeV

Mark Heinz

University of Bern, Switzerland

For the STAR collaboration

HotQuarks

Taos NM, July 2004

contents
Contents
  • Motivation
  • STAR Results
  • Experimental comparisons
  • PYTHIA comparisons
  • Summary

Mark Heinz

motivation
Motivation
  • P-P collisions are a baseline to compare heavy-ion results to
  • Study pQCD (PYTHIA) mini-Jet production in a “clean” environment
  • Study systematic behavior of <pt> vs event multiplicity for strange particles

Mark Heinz

results data sample
Results – Data Sample
  • RHIC Run 2001/2002
  • Total data sample ~14 M events (usable ~ 11M)
  • Trigger: Beam-Beam Counters (BBC)
  • Strange particle PID:
    • Decay topology (V0s, Xis)
    • dE/dx from TPC

Required Correction to raw data:

  • Primary Vertex-efficiency
    • MC-Study
  • Pile-up
    • Vertex matching & CTB (central trigger barrel)
  • Reconstruction efficiency
    • Embedding
  • Feed-down
    • Xi vs Lambda embedding

MC-Study

14% lost vertices

10% fake vertices

PrimVtx position (true-found)

Mark Heinz

particle spectra 1 k0short sd
Composite fit :

mt-exponential (low pt)

& powerlaw (high pt)

Particle Spectra 1: K0short (sd )

|y|<0.5

STAR Preliminary

  • Decay: π-+ π+ (br. 64%)
  • dN/dy = 0.128 ± 0.008
  • <pt> = 0.603 ± 0.006
  • Systematic Errors:
  • <pt> : 2% (Cuts) + 4% (Fit)
  • Yield: 11% (Cuts) + 4% (Fit)

Low Pt acceptance : 150Mev

UA5-Comparison (|y|<2.0):

<pt> = 0.53 +0.08,-0.06

dN/dy = 0.11 +- 0.05

Mark Heinz

particle spectra 2 lambda uds
Particle Spectra 2: Lambda (uds)

STAR Preliminary

  • Decay: p+ π- (br. 68%)
  • dN/dy = 0.086 ± 0.007
  • FD corrected = 0.066 ± 0.004
  • <pt> = 0.76 ± 0.05
  • Ratio = 0.90 ± 0.02

Composite fit: mt-exp & pt-exp

|y|<0.5

UA5-comparison (|y|<2.0)

<pt> = 0.8 +0.2,-0.14

dN/dy = 0.08 ± 0.02

Systematic Errors:

<pt> : ~10 %, Yield: ~15 %

Low Pt acceptance : 300 Mev

Mark Heinz

particle spectra 3 xi dss
Particle Spectra 3: Xi- (dss)

Decay: Λ+ π- (br. 99.9%)

dN/dy = 0.0018 ± 0.0002

<pt> = 0.96 ± 0.05

Ratio = 0.90 ± 0.05

UA5-comparison (|y|< 3.0)

<pt> = 0.8 +0.4,-0.2

dN/dy = 0.0025 ± 0.0015

Low Pt acceptance : 500 MeV

Systematic Errors:

<pt> : ~20 %, Yield: ~40 %

Mark Heinz

omega and anti omega
Omega and Anti-Omega
  • Not enough statistics for pt-spectra
  • Anti-particle/particle Ratio is 0.9+-0.1

Mark Heinz

pt vs particle mass
<pt> vs particle mass
  • Measured particles over large mass range
  • Mass dependence, but not from flow
  • Nice agreement with phenomenological curve established by ISR (25GeV)
  • Strange baryons and resonances are above the curve

Mark Heinz

multiplicity dependence of pt
Multiplicity dependence of <pt>
  • How to define Multiplicity ?
  • Definition of Ncharge is experiment dependant (pseudo-rapidity acceptance coverage)

Mark Heinz

mini jet theory hijing wang gyulassy
Mini-Jet Theory/HIJING (Wang&Gyulassy)

Ncharge distribution for 200 GeV (UA5)

  • Mini-jet X-section becomes significant at √200 GeV
  • Geometrical scaling breaks (ratio of σinel / σelastic non-constant)
  • Inelastic X-section:
    • σinel = ΣσnJet

NJet=1

Contribution of Mini-jets is considerable at n>30.

NJet=2

PRD 45,844 (1992)

Mark Heinz

pt vs n charge fermilab ua1
<pt> vs Ncharge : FermiLab – UA1

1992: E735 Fermilab

p+p – 1.8 TeV

1996: CERN SPS UA1

p+p – 630 GeV

Δ (<pt>Pbar ) ~ 25%

Δ (<pt> Kch ) ~ 20%

Δ (<pt>Lambda ) ~ 55%

Δ (<pt> K0s ) ~ 50%

-0.36< η < 1.0

Lambda

55%

K0s

RHIC prediction

50%

h-

K0s: | η |<2.5, Lambda: |η|<2.0

Pt-Coverage: 0.4-7.0 GeV/c

Fitfunction: Powerlaw(K0s), pt-Exp (Lambda)

Phys Lett B 336 (1996)

Pt-Coverage: 0.2-1.5 GeV/c

Nch measured over 6.5 units η

Fit: pt-exp

Phys Lett B 282 (1992)

Mark Heinz

pt vs multiplicity star
<pt> vs multiplicity: STAR

Composite fit

Powerlaw fit

Mt-exponential fit

  • Measurement is dependant on the parameterization used (fit function to spectra)
  • Increase in <pt> for Lambda (35%) is stronger than for K0s (20%)

STAR Preliminary

STAR Preliminary

Lambda

K0Short

Δ <pt> ~ 35%

Δ <pt> ~ 20%

Mark Heinz

mini jets in pythia

Parton <pt> vs Multiplicity

Pt correlation Parton/Final

Mini-Jets in PYTHIA
  • String fragmentation (Lund Model)
  • Pythia-Settings (6.2/MSEL1)
  • Correlations between pt of hard parton process and event multiplicity
  • Correlation between pt of parton process and final state pt

Mark Heinz

pythia pt spectra
Spectra at mid rapidity

|y|<0.5 (K0s,Lambda)

|y|<0.75 (Xi)

PYTHIA and data disagree in:

Shape of pt-spectra & <pt>

Yield

PYTHIA: Pt-Spectra

Xi

K0short

Lambda

Data

Pythia

Data

Pythia

Data

Pythia

Mark Heinz

pythia pt vs multiplicity
PYTHIA: <pt> vs multiplicity

K0short

Lambda

  • Systematic & statistical errors shown
  • PYTHIA underpredicts the magnitude and correlation strength between <pt> and multiplicity for measured strange particles

Recently CDF (Fermilab) has also shown the discrepancy between PYTHIA

And data for <pt>h+- vs Nch (PRD 65,2002)

Mark Heinz

summary
Summary
  • Highest statistics measurement in p+p (200GeV) of neutral strange and multi-strange particles
  • Yield and <pt> are consistent with previous measurements from UAx/Fermilab experiments
  • PYTHIA fails to describe the shape of the spectra and the multiplicity dependence of <pt>

Future Work

  • More work to be done to get <pt> of Xi and Φ as function of multiplicity
  • Long Paper is in the works for publication this fall

Mark Heinz

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